Because the letter to Grassley specifically said Huber would report on his findings. I would think it would be in writing.
Grassley needs to get Sessions in front of him again and demand an update. Among other things.
No indication in the March 29 letter that Huber would make a public report.
Sessions said “upon conclusion of his review, will receive his recommendations”.
https://cdn.cnn.com/cnn/2018/images/03/29/ag.letter.re.ig.and.huber.reviews.pdf